Add box plot analysis

Add an extra worksheet in which changes in temperature and precipitation are presented in summary form as box plots

Steps:
1. select homogenouse regions
2. calculate the changes in the variables for all GCMs and RCM pairs
3. plot as box and whisker plots

No file or test is named. Start by locating the existing worksheets and the code that selects homogeneous regions and calculates temperature and precipitation changes for GCM/RCM pairs. Add an extra worksheet with box-and-whisker plots, then verify that the requested changes are summarized for all applicable model pairs.

Written by the indexing model from the issue text.